The present invention relates to methods and systems for inspecting turbine blade internal cooling features using non-contact scanners.
A gas turbine engine, such as a turbo fan engine for an aircraft, commonly includes a fan section, a compression section, a combustion section and a turbine section. The engine has a centrally located axis, which extends longitudinally through the sections. The primary flow path for working medium gases extends axially through the sections of the engine. A secondary flow path for working medium gases extends parallel to and radially outward of the primary flow path.
During engine operation, the fan draws the working medium gases, for example air, into the engine. The fan raises the pressure of the air drawn along the secondary flow path, producing useful thrust. The air drawn along the primary flow path into the compression section is compressed. The compressed air is channeled to the combustion section where fuel is added to the compressed air and the air/fuel mixture is burned. The products of combustion are discharged to the turbine section. The turbine section extracts work from these products to power the fan and compressor. Energy in excess of that required to power the fan and compressor contributes to useful thrust.
In order to withstand the extreme operating temperatures in gas turbine engines, some of the rotor blades and stator vanes (hereinafter referred to as “blades”) in the compressor and turbine sections are internally cooled with bleed air drawn from, for example, the compressor. Internally cooled blades commonly include internal features, such as turbulators and trip strips, designed to increase cooling efficiency. Blade internal cooling features are generally in the form of protrusions of various sizes and shapes extending into the blade cavity from one internal wall or connected between both internal walls of the blade.
Various testing and quality assurance measures included in the manufacture and repair of internally cooled gas turbine blades necessitate measurement of the blade internal cooling features. Prior methods of and systems for inspecting the internal cooling features of blades commonly include predominately manual procedures, which are labor intensive and require complex set-up procedures poorly adapted for repeatability. For example, prior methods include scribing the geometry of one or more internal features by running a stylus over the feature and measuring the displacement of the stylus to extrapolate the feature geometry. Scribing the geometry of internal blade features has several disadvantages. Internal cooling features of gas turbine blades are often relatively small, for example, having a height in the range of approximately 0.01 to 0.02 inches (0.254 to 0.508 millimeters). Scribing the geometry of such small features may be prone to serious error, as it is possible for the stylus to jump over the features without accurately scribing their entire contour. Moreover, the accuracy of the inspection is dependent upon the size of the stylus tip, which may not be small enough to, for example, scribe a feature edge with a small radius. Another prior method includes projecting light onto the blade feature to create a shadow of the feature and manually tracing and measuring the feature shadow. In both of the aforementioned examples, the internal features of the blade must be exposed by removing one or more portions of the blade exterior, for example by wire cutting the blade in half. Additionally, the blade must be precisely oriented to accommodate the manual or machine assisted measurement of the internal feature geometry. Properly orienting the blade for inspection often requires special fixtures, which may depend on the particular blade and internal feature configuration inspected and the method of inspection employed.